Touch PDF optimized for Kobo Touch.

[Obok]

Hello,

I bought a Kobo touch, and is really satisfied. I have a question. Please help me, guys.
I wanna enjoy side-loaded PDFs which are generated from scanning printed books. To reduce the white margins and file size, I adjust scanned pictures to KoboT. As you know, it is important to fit very accurately the size( actually pixel resolution I mean ) to the Kobo's eInk screen in order to reducing jaggies. Maybe many Alphabet users don't care such a small jaggies, but Japanese needs to read intricate Kanji characters, maybe Chinese too.

This way works very well for Sony reader and Nook touch, and maybe Kindle. But I CAN'T know the best size for KoboT. In my experience, KoboT always drops some bottom lines from the screen. I found that 600x750cross-hatching + 49bottom-margin works well. But it seems to change for other pictures. And, more complicated, once you zoom it and back to 100%, it's no longer fit the screen.
How can I generate Kobo optimized PDFs?